1. Field of the Invention
The present invention relates to a method and apparatus for system encoding bitstreams for seamless connection and, more specifically, to bitstreams for use in an authoring system for variously processing a data bitstream comprising the video data, audio data, and sub-picture data constituting each of plural program titles containing related video data, audio data, and sub-picture data content to generate a bitstream from which a new title containing the content desired by the user can be reproduced, and efficiently recording and reproducing the generated bitstream using a particular recording medium.
2. Description of the Prior Art
Authoring systems used to produce program titles comprising related video data, audio data, and sub-picture data by digitally processing, for example, multimedia data comprising video, audio, and sub-picture data recorded to laser disk or video CD formats are currently available.
Systems using Video-CDs in particular are able to record video data to a CD format disk, which was originally designed with an approximately 600 MB recording capacity for storing digital audio data only, by using such high efficiency video compression techniques as MPEG. As a result of the increased effective recording capacity achieved using data compression techniques, karaoke titles and other conventional laser disk applications are gradually being transferred to the video CD format.
Users today expect both sophisticated title content and high reproduction quality. To meet these expectations, each title must be composed from bitstreams with an increasingly deep hierarchical structure. The data size of multimedia titles written with bitstreams having such deep hierarchical structures, however, is ten or more times greater than the data size of less complex titles. The need to edit small image (title) details also makes it necessary to process and control the bitstream using low order hierarchical data units.
It is therefore necessary to develop and prove a bitstream structure and an advanced digital processing method including both recording and reproduction capabilities whereby a large volume, multiple level hierarchical digital bitstream can be efficiently controlled at each level of the hierarchy. Also needed are an apparatus for executing this digital processing method, and a recording media to which the bitstream digitally processed by the apparatus can be efficiently recorded for storage and from which the recorded information can be quickly reproduced.
Increasing the storage capacity of conventional optical disks has been widely researched to address the recording medium aspect of this problem. One way to increase the storage capacity of the optical disk is to reduce the spot diameter D of the optical (laser) beam. If the wavelength of the laser beam is 1 and the aperture of the objective lens is NA, then the spot diameter D is proportional to 1/NA, and the storage capacity can be efficiently improved by decreasing 1 and increasing NA.
As described, for example, in U.S. Pat. No. 5,235,581, however, coma caused by a relative tilt between the disk surface and the optical axis of the laser beam (hereafter "tilt") increases when a large aperture (high NA) lens is used. To prevent tilt-induced coma, the transparent substrate must be made very thin. The problem is that the mechanical strength of the disk is low when the transparent substrate is very thin.
MPEG1, the conventional method of recording and reproducing video, audio, and graphic signal data, has also been replaced by the more robust MPEG2 method, which can transfer large data volumes at a higher rate. It should be noted that the compression method and data format of the MPEG2 standard differ somewhat from those of MPEG1. The specific content of and differences between MPEG1 and MPEG2 are described in detail in the ISO-11172 and ISO-13818 MPEG standards, and further description thereof is omitted below.
Note, however, that while the structure of the encoded video stream is defined in the MPEG2 specification, the hierarchical structure of the system stream and the method of processing lower hierarchical levels are not defined.
As described above, it is therefore not possible in a conventional authoring system to process a large data stream containing sufficient information to satisfy many different user requirements. Moreover, even if such a processing method were available, the processed data recorded thereto cannot be repeatedly used to reduce data redundancy because there is no large capacity recording medium currently available that can efficiently record and reproduce high volume bitstreams such as described above.
More specifically, particular significant hardware and software requirements must be satisfied in order to process a bitstream using a data unit smaller than the title. These specific hardware requirements include significantly increasing the storage capacity of the recording medium and increasing the speed of digital processing; software requirements include inventing an advanced digital processing method including a sophisticated data structure.
Therefore, the object of the present invention is to provide an effective authoring system for controlling a multimedia data bitstream with advanced hardware and software requirements using a data unit smaller than the title to better address advanced user requirements.
To share data between plural titles and thereby efficiently utilize optical disk capacity, multi-scene control whereby scene data common to plural titles and the desired scenes on the same time-base from within multi-scene periods containing plural scenes unique to particular reproduction paths can be freely selected and reproduced is desirable.
However, when plural scenes unique to a reproduction path within the multi-scene period are arranged on the same time-base, the scene data must be contiguous. Unselected multi-scene data is therefore unavoidably inserted between the selected common scene data and the selected multi-scene data. The problem this creates when reproducing multi-scene data is that reproduction is interrupted by this unselected scene data.
A further problem can be expected when the multi-scene data is multi-angle scene data, i.e., scene data showing substantially the same subject from different angles. In the case of a live sports broadcast, this multi-angle scene data may be obtained by recording a baseball batter, for example, with cameras in different locations. The video signals from these plural angles are then combined in predefined data units to obtain a single title. Specifically how these plural video streams will be connected and reproduced, however, cannot be determined during the encoding process. As a result, the behavior of the decoder video buffer, specifically the data accumulation state of the video buffer during the decoding process, cannot be determined during the encoding process. As a result, a video buffer overflow or underflow state may occur during decoding. Even at one-to-one connections between common scenes (system streams), the behavior of the decoder video buffer cannot be determined during encoding.
When variable length coding is used for the coding process, the process must always proceed in a time-base linear fashion. This makes it necessary to control the sequence of the coding process, and limits the flexibility of the title production process. In addition, there are cases in which the final buffer occupancy during first video stream encoding exceeds the initial buffer occupancy of the second video stream. In such cases, a decoding buffer overflow may occur at some indeterminate time during the coding process.
When MPEG coding or a similar variable length coding process is used during the coding process generating the video stream, the coded data quantity is only known once the coding process is completed. This is because the coding length used is determined according to the amount of information in the video data, i.e., the spatial complexity or time-base complexity of the video data, and the preceding code state, and the code length is then determined. Because it is therefore difficult to accurately limit the encoded data size to a specific, predetermined size, it is difficult to accurately specify the final buffer occupancy. Particularly when the encoded data volume is allocated and the coding process is accomplished according to the amount of information in the video stream, the allocated data volume will obviously vary if the amount of information in the video stream changes, and the change in video buffer occupancy will vary. It is therefore difficult to assure that the final decode video buffer occupancy is the same with each of plural video streams.
Therefore, the object of the present invention is to provide a coding method and coding apparatus, a recording method and recording apparatus, and a reproduction method and reproduction apparatus whereby plural independently coded video streams can be freely connected and reproduced without causing a video buffer overflow or underflow state.
A further object of the present invention is to provide a coding method and coding apparatus, a recording method and recording apparatus, and a reproduction method and reproduction apparatus whereby the need for the coding process to proceed in a linear time-base fashion to obtain each video stream is eliminated, the processing time can be shortened by means of parallel coding processes, and process control can be simplified when plural video streams are connected to obtain a single video stream.
A further object of the present invention is to provide a coding method and coding apparatus, a recording method and recording apparatus, and a reproduction method and reproduction apparatus whereby video streams from plural reproduction paths are coded to a multi-scene period from which the user can select a particular reproduction path during reproduction, and the desired video streams from the multi-scene period containing plural selectable video streams (reproduction paths) can then be individually reproduced and contiguously presented as a single video stream without causing a video buffer overflow or underflow state during the decoding (reproduction) process.
The present application is based upon Japanese Patent Application No. 7-252736 and 8-041582, which were filed on Sep. 29, 1995 and Feb. 28, 1996, respectively, the entire contents of which are expressly incorporated by reference herein.